1. Industrial Field of the Invention
The present invention relates to a method of manufacturing a liquid crystal display panel, and also relates to a liquid crystal display panel apparatus having an improved image quality.
2. Description of the Prior Art
A typical twist-nematic liquid crystal display panel is, for example, constituted as shown in FIG. 12. In such conventional display panel, an upper substrate 3 is formed with a color filter 2 thereon and a lower substrate 5 is formed with picture element electrodes 4 thereon, between which liquid crystal 1 is interposed. Polarizing plates 6 and 7 are located respectively on the outsides of the upper and the lower substrates 3 and 5. In order to apply orientation to the liquid crystal 1, the upper and the lower substrates 3 and 5 are coated with an alignment film of polymeric materials (for example, polyimide and so on) and rubbed with cloths. The directions of rubbing the upper and the lower substrates 3 and 5 cross each other at an angle of 90.degree. . For this reason, molecules of the liquid crystal 1 are arranged along the alignment directions of the upper and the lower substrates and the arrangements are twisted as shown in FIGS. 13a and 13b. The twisted directions of the arrangements of the molecules of the liquid crystal should be the same anywhere in the liquid crystal display panel. However, a defect, referred to as a reverse domain in which the twisted direction is reversed, partially takes place due to a flowing effect when pouring the liquid crystal 1 into the panel. Ordinarily, as a measure to cope with this defect, a well known method is to fill the liquid crystal 1 into the panel after raising the temperature thereof higher than the N-I point (a transformation point from a nematic phase to an isotropic phase and at the temperature of the N-I point, the liquid crystal 1 becomes isotropic and transparent), that is to say, after making the liquid crystal 1 isotropic. Another method is to pour the liquid crystal 1 into the panel, prior to heating in order to make the liquid crystal 1 isotropic, and then to avoid causing the reverse domain by naturally cooling the liquid crystal 1.
A liquid crystal display panel has been manufactured by the above-described conventional method without hindrance. However, whereas a tendency toward high definition images has recently advanced, and a liquid crystal display panel of an active matrix type in which every picture element is provided with a thin film transistor has been developed. Further, an area of the picture element is decreased so as to increase the density of the panel. In this case, as shown in FIG. 14, the smaller the area of the picture element, the less the contact force of the rubbing cloth against the picture element surface becomes due to convex or concave portions formed by the thin film transistor 9 and a source wiring 10. As a result, the strength of orientation of the liquid crystal 1 is weakened and the reverse domain can easily occur. It is impossible to eliminate the weakness in orientation force of the liquid crystal and the occurrence of the reverse domain due to the configurational effect of the convex or concave portions formed by the thin film transistor and the source wiring, through the conventional heat treatment method.
As a measure of coping with this reverse domain, a method has conventionally been employed such that a swirling force of the liquid crystal is strengthened by adding to the liquid crystal a small amount of swirling material referred to as cholesteric liquid crystal (for example, CB15; CHISSO CORPORATION). Too great an increase in the amount of the swirling material added to the liquid crystal results in a characteristic deterioration so that a rate in responsibility of the liquid crystal is decreased. Therefore, there is a limit to which this material may be added.
As disclosed in the liquid crystal display panel apparatus (Japanese Patent Unexamined Publication No. 59-21380), there has been also proposed a method in which the liquid crystal molecules are arranged in bilateral helical rotational directions. However, the results of this method are not fully known or predictable.